Internet DRAFT - draft-ietf-ipngwg-ipaddressassign
draft-ietf-ipngwg-ipaddressassign
Network Working Group M. Blanchet
Internet-Draft Viagenie inc.
Expires: August 31, 2001 March 2, 2001
A flexible method for managing the assignment of bits of an IPv6
address block
draft-ietf-ipngwg-ipaddressassign-02
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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This Internet-Draft will expire on August 31, 2001.
Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
This document presents a method to manage the assignment of bits of
an IPv6 address block or range. When an organisation needs to make
an address plan for its subnets or when an ISP needs to make an
address plan for allocating address ranges to its customers, this
method enables the organisation to postpone the final decision on
the number of bits to partition in the address space they have. It
does it by keeping the bits around the borders of the partition to
be free as long as possible. This scheme is applicable to any bits
addressing scheme using bits with partitions in the space, but its
first intended use is for IPv6. It is a generalization of RFC1219
and can be used for IPv6 assignments based on RFC2373 and RFC2374.
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Table of Contents
1. Rationale . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Address plan . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1 leftmost . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2 rightmost . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3 centermost . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Implementation . . . . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 12
Full Copyright Statement . . . . . . . . . . . . . . . . . . . 13
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1. Rationale
IPv6 addresses have a more flexible structure for address
assignments than IPv4 where no pre-defined prefixes (called
subnetmasks in IPv4) are used (except a few special cases). It
enables registries, internet service providers, network designers
and others to assign addresses ranges to organisations and networks
based on different criterias, like size of networks, estimated
growth rate, etc. Often, the initial assignation doesn't scale well
because a small network becomes larger than expected, needing more
addresses. But then, the assignment autority cannot allocate
contiguous addresses because they were already assigned to another
network.
RFC1219 describes an allocation scheme for IPv4 where address space
is kept unallocated between the leftmost bits of the subnet part and
the rightmost bits of the host part of the address. This enables the
network designer to change the subnetmask without renumbering, for
the central bits that were not allocated.
This work generalizes the previous scheme by extending the algorithm
so it can be applied on any part of an IP address, which are
assigned by any assignment autority level (TLA, registries, ISPs,
organisations, ...). It can be used for both IPv4 and IPv6, with
IPv6 assignments conforming to RFC2373 and RFC2374.
This document is not an IPv6 address allocation plan, but can be
used as a method for allocation plans, and is independent of any
specific internet address registry ipv6 allocation plan.
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2. Scheme
We define parts of the IP address as p1, p2 , p3, ... pN in order,
so that an IP address is composed of these parts contiguously.
Boundaries between each part are based on the prefix assigned by the
next level assignment autority. Part p1 is the leftmost part
probably assigned to a TLA, Part p2 can be assigned by the TLA to a
large internet service provider or to a national registry. Part p3
can be allocated to a large customer or a smaller provider, etc.
Each part can be of different length. We define l(pX) the length of
part X.
+------+------+------+------+------+------+
| p1 | p2 | p3 | p4 | ... | pN |
+------+------+------+------+------+------+
<------- ipv6 or ipv4 address ------------>
The algorithm for allocating addresses is as follows : a) for the
leftmost part (p1), assign addresses using the leftmost bits first
b) for the rightmost part (pN), assign addresses using the rightmost
bits first c) for all other parts (center parts), predefine an
arbitrary boundary (prefix) and then assign addresses using the
center bits first of the part being assigned.
This algorithm grow assigned bits in such way that it keeps
unassigned bits near the boundary of the parts. This means that the
prefix between any two parts can be changed forward or backward,
later on, up to the assigned bits.
Any assignment must conform to RFC2373 and RFC2374, which have
precedence over this method in case of conflicts.
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3. Address plan
3.1 leftmost
p1 will be assigned in order as follows :
Order Assignment
1 10000000
2 01000000
3 11000000
4 00100000
5 10100000
6 01100000
7 11100000
8 00010000
9 ...
This is actually a mirror of binary counting.
3.2 rightmost
pN (the last part) will be assigned in order as follows :
Order Assignment
1 00000001
2 00000010
3 00000011
4 00000100
5 00000101
6 00000110
7 00000111
8 00001000
9 ...
3.3 centermost
pX (where 1 < X < N) will be assigned in order as follows : (for
example, with a 8 bit predefined length l(pX)=8))
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Order Assignment
1 00001000
2 00010000
3 00011000
4 00000100
5 00001100
6 00010100
7 00011100
8 00100000
9 ...
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4. Example
A TLA has been assigned the 3ffe:0b00/24 prefix and wants to assign
prefixes to its connected networks. It anticipates in the forseable
future a maximum of 256 NLAs consuming 8 bits. One of these NLA,
named NLA2, anticipates a maximum of 1024 subNLA assignments under
it, consuming 10 other bits.
The assignment will be as follows, not showing the first 24 leftmost
bits (3ffe:0b00/24: 00111111 11111110 00001011):
TLA assigning to NLAs using lefmost bits:
10000000 : assigned to NLA1
01000000 : assigned to NLA2
11000000 : assigned to NLA3
00100000 : assigned to NLA4
...
NLA2 assigning to its subNLAs using centermost bits:
0000010000 : assigned to subNLA1
0000100000 : assigned to subNLA2
0000110000 : assigned to subNLA3
...
subNLAs can use centermost bits for maximum flexibility and then the
last aggregators (should be a network in a site) will be assigned
using rightmost bits.
Putting all bits together for subNLA3:
TLA |NLA2 |subNLA3
00111111 11111110 00001011 01000000 00001100 00
<-------> <------>
growing bits
By using this method, the TLA will be able to expand the number of
NLAs and the NLAs will be able to modify their first assumptions
about the size of their subNLAs, until "reserved" bits are assigned.
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5. Implementation
The following perl code was written by Jocelyn Picard
(Jocelyn.Picard@viagenie.qc.ca) and implements this draft.
#!/usr/bin/perl -w
use strict;
#===============================================================================
# allocation(Last Prefix,Number of bits,Method)
#
# Last Prefix = last prefix allocated, ex: 3ffe:b00::/48
# Number of bits = range we want to allocate
# Method = method to use: l,c or r (left,center,right)
#
# Returns next prefix using selected method
#
# Note: no validation is made
#
#---------------------------------------------------------------------
sub allocation {
my ($ip,$pl)=split('/',shift);
my ($nbits,$method) = @_ ;
my ($w,@Abits,$abits);
my $i = $ip =~ s/:/:/g;
my $repl= ':0' x (9 - $i);
$ip =~ s/::/$repl/;
$ip =~ s/^:/0:/;
foreach $i (split(':',$ip)) {
push @Abits, split('',unpack("B16", pack("n", hex($i))));
}
my $sp = int($nbits/2);
for($i=0;$i<$nbits;$i++) {
if ($method eq "c") {
$w = ($i % 2) ? $sp - ($i+1)/2: $sp + $i/2;
}
elsif ($method eq "r") {
$w = $nbits -1 - $i;
}
else {
$w = $i ;
}
$w += $pl - $nbits;
if ($Abits[$w] == 0) {
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$Abits[$w] = 1;
last;
}
else {
return 0 if ($i == $nbits-1);
$Abits[$w] = 0;
}
}
$abits = join("",@Abits);
$ip = "";
for($i=0;$i<8;$i++) {
$ip .= sprintf("%lx", unpack("n", pack("B16", substr($abits, $i * 16,16)))) . ":";
}
chop $ip;
$ip =~ s/(:0){2,}$/::/;
return($ip . "/$pl");
}
#===============================================================================
#
#Usage example: allocation of 100 /48 using "centermost" method
#
my $Prefix = '3ffe:b00::/48';
for(my $i=0;$i<100;$i++) {
print $Prefix = allocation($Prefix,16,'c'),"\n";
}
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6. Security Considerations
Address assignment doesn't seem to have any specific security
consideration.
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7. References
[1] RFC2373 IP Version 6 Addressing Architecture. R. Hinden, S. Deering. July
1998. (Format: TXT=52526 bytes) (Obsoletes RFC1884) (Status: PROPOSED
STANDARD)
[2] RFC2374 An IPv6 Aggregatable Global Unicast Address Format. R. Hinden, M.
O'Dell, S. Deering. July 1998. (Format: TXT=25068 bytes) (Obsoletes
RFC2073) (Status: PROPOSED STANDARD)
[3] RFC1219 On the assignment of subnet numbers. P.F. Tsuchiya. Apr-01-1991.
(Format: TXT=30609 bytes) (Status: INFORMATIONAL)
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8. Acknowledgements
Thanks to Steve Deering, Bob Hinden, Erik Nordmark, Florent Parent
and Jocelyn Picard for their very useful comments on this work.
Author's Address
Marc Blanchet
Viagenie inc.
2875 boul. Laurier, bureau 300
Sainte-Foy, QC G1V 2M2
Canada
Phone: +1 418 656 9254
EMail: Marc.Blanchet@viagenie.qc.ca
URI: http://www.viagenie.qc.ca/
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Full Copyright Statement
Copyright (C) The Internet Society (2001). All Rights Reserved.
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Acknowledgement
Funding for the RFC editor function is currently provided by the
Internet Society.
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